1. Field of the Invention
This invention pertains generally to liquid sprayer systems and more particularly to the on-demand metering, mixing, atomization and dispersal of a number of liquid components in a single spray liquid mixture.
2. Description of Related Art
Modern agriculture is becoming increasingly dependent on the efficient and accurate application of liquid fertilizers and crop protection agents in order to be profitable and environmentally responsible. Agricultural chemicals may be applied as sprays of liquid solutions, emulsions or suspensions from a variety of delivery systems. Typical systems pressurize liquid from a reservoir and atomize a liquid stream into droplets through a nozzle. Nozzles may be selected to provide a range of droplet sizes, spray distribution patterns and flow rates for a desired liquid material application. Spray distribution, droplet size, droplet velocity and flow rate are important considerations in field applications. Ideally, sprays of properly sized droplets will produce uniform coverage of material over the vegetation, the ground or other substrate. Spray distribution is the uniformity of coverage and the pattern and size of the spray area, including the overlap of spray patterns between nozzles. Poor spray distribution can limit the efficacy of an application and may lead to adverse environmental injuries, poor crop yields and increased costs.
In agricultural spraying, the applied liquid often contains a number of constituents that are mixed prior to application. Once mixed in a central reservoir, the concentration and relative ratios of the individual components in the carrier liquid cannot be altered and the mix may have a limited tank life. Additionally, some constituents, either active ingredients, inert materials in the pesticide formulations or adjuvants selected by the applicator, may be chemically or physically incompatible and not mix properly.
Chemical injection systems, where carrier fluids, active ingredients and adjuvants are mixed during application, rather than prior to application, have been developed and marketed for agricultural spraying. In these systems, a central pump propels the carrier fluid, consisting of the primary diluent, often water, and perhaps a mixture of compatible materials to the nozzles for distribution. The incompatible fluid components are propelled by separate pumps, from separate reservoirs, and injected into the carrier fluid flow either upstream of the carrier pump or downstream of the carrier pump.
Additionally, it is sometimes desirable to apply some of the spray liquid components only to certain portions of a crop field to be treated. In those situations, the entire mix of spray liquid components is not prepared prior to initiating the spray application job. Rather, the components that are to be applied to certain portions of the field are applied using a separate spray system containing only the component to be applied singularly.
The limitations of common injection systems have been investigated and documented by researchers in the technical field of agricultural spraying. Steward and Humburg (2000), investigating injection system for maintaining a constant deposition rate of spraying as ground speed of a spraying vehicle varied, found that direct injection systems can reduce much of the application rate error that results from variations in the ground speed. They also found that chemical injection with carrier flow rate control resulted in less application error than when the carrier flow rate was held constant and the injected chemical rate varied, as it minimized concentration variations and reduced transport delays.
One disadvantage of some direct injection systems is that the lag time from initiation of an injection chemical rate change to the time when the new rate of chemical actually leaves the nozzles can lead to chemical application rate errors during transient response times.
A commercial injection system has also been proposed for maintaining a constant concentration circulating in a chamber awaiting sensor-triggered spot spraying of weeds. The system maintained a desired concentration over a range of operating conditions.
The fundamental limitation with many commercial injection systems, however, can be due to the basic configuration where the central injection point is located immediately upstream or downstream from the carrier liquid pump. This results in lengthy hose and pipe distances from the injection point to the nozzles. Moreover, the length of fluid passage from the injection point to each nozzle is variable. The consequence of this configuration is that the time delays between changes in injection rate and the arrival of the altered rate at the nozzles are lengthy and vary from nozzle to nozzle. Therefore, application rates of the injected materials are non-uniform across the boom and temporally and spatially variable in an unintended and undesirable manner.
A solution to the problems resulting from a central injection point is to inject materials directly at the nozzle inlet. However, this configuration is not without considerable challenges; pumping and metering of the injected fluid must be distributed along the spray booms and adequate mixing must occur within the nozzle during a brief time period. Crowe et al. (2005) reported the development of an “at-nozzle” conductivity probe for high-speed measurement of transient injection events. Further work by Downey et al. (2006) investigated the use of miniature metering valves at individual spray nozzles. The system provided rapid response for triggered spraying; however, the components were expensive, complex and required a pressurized source of injection liquid near the spray nozzle.
Previous systems addressing injection at the nozzle inlet have required pumping and metering systems and modification of nozzle plumbing. An additional question has related to the degree of mixing within the nozzle before discharge. Pressurized lines of highly concentrated pesticide are often considered a potential hazard.
One type of nozzle that has been used in prior spraying systems is the air induction nozzle. Air induction nozzles are constructed with an embedded Venturi induction port fabricated into the nozzle assembly. The Venturi port creates a vacuum that induces the flow of ambient air into the nozzle, resulting in enlarged droplet size spectra in an attempt to mitigate spray drift, that is, the unintended and undesirable movement of spray droplets away from their intended target. Ambient wind, coupled with small sized droplets, is the prime cause of spray drift.
Air induction nozzles have been used commercially as a simple means of drift reduction in agricultural field spraying. For typical nozzles tested, the degree of air entrainment ranged from 0.2 to 0.61 min−1. Air induction nozzles have shown some ability to control droplet size produced by the nozzles. Droplet size can be affected by the degree of air entrainment and/or by the orifice size of the nozzle. However, sprayer systems using air induction nozzles have the same problems described heretofore as systems using other types of nozzles.
Accordingly, there is a need for a sprayer system in which injection of an agrochemical into a carrier fluid or carrier mixture of fluids can be achieved easily, reliably and without complex components. Moreover, there is a need for a system that reduces time delays between injection and dispersal of the spray mixture and/or one that provides greater uniformity in distribution of chemical mixtures throughout lengthy spray nozzle arrays.